Chemical alteration patterns of ancient Egyptian papyri studied by Pyrolysis-GC/MS with in situ silylation

Analytical pyrolysis-gas chromatography coupled with mass spectrometry with in situ silylation using hexamethyldisilazane (Py(HMDS)-GC/MS) was employed to study a set of ancient Egyptian papyri. The aim was to investigate their chemical alteration patterns and to obtain information regarding the degradation pathways affecting them. In ancient Egypt, papyrus was widely exploited and its most important use was as a writing surface, created from strips of the pith found inside the stalk laid down in layers and dried under pressure. These strips were formed into rolls that were left intact or cut into sheets. From a chemical point of view, papyrus mainly consists of three biopolymers: cellulose, hemicellulose and lignin. Biological degradation due to fungi, bacteria or insects is the main cause of papyri decay in archaeological findings. However, thanks to the dry climate of the desert, the remains of many papyri have been found and recovered in Egypt. Py-GC/MS was used to identify roughly 90 compounds in the pyrograms of the various papyri. In terms of the main pyrolysis products derived from polysaccharides and lignin, compositional differences were detected between the archaeological papyri of several historical periods and sound modern papyrus sheets and plants. These chemical differences were derived from the modifications - such as depolymerisation, oxidation and depletion - undergone by both the polysaccharides and lignin.